The category of range widgets includes the ubiquitous scrollbar widget
and the less common scale widget. Though these two types of widgets
are generally used for different purposes, they are quite similar in
function and implementation. All range widgets share a set of common
graphic elements, each of which has its own X window and receives
events. They all contain a "trough" and a "slider" (what is sometimes
called a "thumbwheel" in other GUI environments). Dragging the slider
with the pointer moves it back and forth within the trough, while
clicking in the trough advances the slider towards the location of the
click, either completely, or by a designated amount, depending on
which mouse button is used.

As mentioned in Adjustments above,
all range widgets are associated with an adjustment object, from which
they calculate the length of the slider and its position within the
trough. When the user manipulates the slider, the range widget will
change the value of the adjustment.

1. Scrollbar Widgets

These are your standard, run-of-the-mill scrollbars. These should be
used only for scrolling some other widget, such as a list, a text box,
or a viewport (and it's generally easier to use the scrolled window
widget in most cases). For other purposes, you should use scale
widgets, as they are friendlier and more featureful.

There are separate types for horizontal and vertical scrollbars.
There really isn't much to say about these. You create them with the
following functions:

and that's about it (if you don't believe me, look in the header
files!). The adjustment argument can either be an
existing Adjustment, or undef, in which case one will be created for
you. Specifying undef might actually be useful in this case, if you
wish to pass the newly-created adjustment to the constructor function
of some other widget which will configure it for you, such as a text
widget.